Accordingly, the invention relates to an antifouling paint that includes a binder of relatively low mechanical strength so that the outer paint layer will be worn away by friction with the water and any organisms that have been able to fasten to the paint layer will be carried away with said layer.
With the intention of reducing the number of organisms that fasten to the surface of an antifouling paint when the boat is generally stationary in the water, it is known to make the layer of the paint applied slippery. Moreover, it is also known to add to the paint one or more additives for further reducing the tendency of the organisms to rest on or fasten to the exposed surface of the self-polishing paint. The biologically active substances that are acceptable from an environmental aspect and which have hitherto been used to control the tendency or ability of marine creatures from fastening to the surface of the self-polishing paint, particularly such creatures as molluscs, barnacles, and the like, have a troublesomely low effect. Although being effective, other substances, for instance metal compounds such as copper oxide or tin salts, or TBT, are generally unacceptable from an environmental aspect.
Accordingly, one object of the present invention is to provide a self-polishing paint which contains an environmentally acceptable substance that is effective in making it difficult for marine organisms, for example molluscs, barnacles, etc. from fastening to the water-exposed paint layer.
Another object of the invention is to provide a self-polishing paint, which also includes a substance that obstructs the process of photosynthesis in respect of algae that have fastened to the surface of the paint. These objects of the invention are achieved, either completely or partially, with a self-polishing antifouling paint.
Another problem is that large ships that require ballast cannot discharge the ballast water within 3 kilometers from a harbor without first cleaning it from alien species according to the new IMO regulation. This means ships must discharge the ballast water and then travel to the harbor without the ballast which makes the ships less stable. Many techniques have unsuccessfully been tried in the past to solve the problem concerning ballast water cleaning. For example, filtering systems have turned out to be ineffective and energy demanding.
The addition of chemicals to the ballast water is also unsatisfactory because the chemicals poison the water prior to discharge into the ocean. Ultraviolet light is also being used but poisonous bromide substances have a tendency to be formed. In view of the above, there is a need for an inexpensive and reliable system that permits ships to discharge ballast water at the harbor while conforming to rules and regulations such as those set out by the IMO.
The method of the present invention provides a solution to the above problems. More particularly, the method is for treating ballast water of a marine vessel. Ballast water is injected into a container of the marine vessel. The ballast water contains multi- and uni-cellular organisms. An organic substance is added to the ballast water so that heterotrophic organisms, such as aerobic and anaerobic bacteria, in the ballast water reproduce and consume the organic substance. In that process, the heterotrophic organisms substantially reduce the oxygen level in the ballast water compared to the oxygen level of untreated ballast water. The heterotrophic organisms consume virtually all the organic substance. Heterotrophic organisms and any other alien multi-cellular organisms die due to lack of oxygen and organic substance.